The Optical Fiber Communications Conference and Exhibition (OFC) is celebrating 50 years of optical networking and communications this year. The milestone highlights decades of innovation from companies such as Acacia that have delivered optical networking technology enabling network operators to continually expand their bandwidth, deliver faster networks, and offer more services.

One of those innovations that we believe will be a dominant topic at OFC this year is coherent optics. Coherent pluggable modules have been critical for enabling network operators to keep up with bandwidth demands over the last decade, and according to Cignal AI, they will account for most of the future bandwidth growth driven by applications such as generative AI and machine learning. Acacia pioneered the coherent pluggable more than 10 years ago with the introduction of the industry’s first 100G CFP module in 2014 and has been a market leader ever since having shipped half a million 400G ports based on the Greylock DSP, including more than 25,000 Bright 400ZR+ ports.

Acacia continues to innovate and will illustrate its industry-leading optical networking advancements through the following demonstrations and speaking sessions:

Demonstrations:

• 200G per lane optical engine products – Demonstrating the recently announced 200G/lane silicon photonics optical engine with transmitter and receiver designs supporting DR4, DR8 and 2xFR4 configurations.
• Delphi DSP-based Coherent Pluggable Portfolio including new L-Band 400G ULH – Showcasing Acacia’s broad 400G module portfolio powered by Acacia’s 9th generation DSP Delphi including 800ZR, 800G ZR+ with interoperable Probabilistic Constellation Shaping (PCS), and 400G Ultra Long Haul. 400G modules in QSFP-DD form factor and 800G modules in both OSFP and QSFP-DD form factors are available with C and L-Band versions.
• OIF multi-vendor interoperability (Booth #5745) – Showing interoperability of 800ZR, 400ZR, OpenZR+ and Multi-Span Optics enhancing multi-vendor interoperability in high-capacity, long-distance optical networks and Common Management Interface Specification (CMIS) standardizing the management of optical and electrical devices to simplify scalability.
• OpenROADM compliant 800G ZR+ coherent modules – Featuring a link between the OIF booth (#5745) and OpenROADM booth (#5128) demonstrating the high-performance interop PCS interface which expands the market for 800G pluggables beyond metro DCI into regional and even long-haul networks. Acacia’s award-winning 800G ZR+ modules were the first in the industry to support the OpenROADM specification.
• Ethernet Alliance (Booth #5173) – Showing interoperability of Acacia 800G ZR interconnects.

Speaking Sessions:

Monday, March 31

• Optica Executive Forum: Status of Photonic-enabled Modules and Interconnects
  — Speaker: Tom Williams, VP of Marketing
  — Time: 10:35-11:50 am
  — Location: Marriott Marquis
• Multi-rate PAM4 Silicon Photonic Based Receiver Assembly with -10dBm iFEC Sensitivity at 226Gb/s/λ and 125mW/Ch CMOS TIA
  — Speaker: Mahdi Parvizi, Principal Engineer
  — Time: 10:30 am to 12:30 pm
  — Location: Rooms 211-212 (Level 2)

Tuesday, April 1

• Market Watch: Optical Modules, Transceivers and Applications
  — Speaker: Tom Williams, VP of Marketing
  — Time: 2:15 – 3:45 pm
  — Location: Theater I

Wednesday, April 2

• Network Operator Summit: Interoperation of Optical Pluggable Transceivers and IP/Optical Integration
  — Moderator: Anuj Malik, Director, Product Management and Strategy
  — Featured speakers from Cignal AI, Arelion, Cox Communications, Deutsche Telekom Technik GmbH, Telefonica
  — Time: 10:45 – 12:15 pm
  — Location: Theater I
• Coherent Optics Unleashed: 400ZR Success to 800ZR/LR Advancements and 1600ZR/ZR+ Kick-Off
  — Speaker: Doug Cattarusa, Technical Marketing Engineer
  — Time: 4:00 – 5:00 pm
  — Location: Theater I

Thursday, April 3

• Market Watch: Optical Network Evolution for AI/ML, Architectures and Drivers
  — Speaker: Tom Williams, VP of Marketing
  — Time: 10:15 – 11:45 am
  — Location: Theater I
• Demonstration of 400G Optical Interoperability in IP Over WDM Network Scenarios Over Single Span WDM System with and Without Optical Amplifiers
  — Speaker: Anuj Malik, Director, Product Management & Strategy
  — Time: 10:30 am
• Coherent Moving to Client Optics
  — Moderator: Tom Williams, VP of Marketing
  — Time: 2:00 – 3:00 pm
  — Location: Theater II

Come See us!
If you are attending OFC 2025 and would like to discuss any of these topics, contact us to request a meeting.

While the near-term focus has been on how AI will affect the technology around short reach interconnects, there will certainly be an impact to interconnections beyond the AI clusters and beyond the AI data center, in hyperscaler networks.

The question is:  beyond the short-distance high-bandwidth interconnections, how would AI traffic impact the optical transport environment beyond the intra-building network and into the metro, long haul, and longer reach applications where optical coherent transmission is heavily utilized?

Figure 1.  Sales Forecast for Ethernet Optical Transceivers for AI Clusters (July 2024 LightCounting Newsletter, “A Soft Landing for AI Optics?”).

Effect of Past Applications on the Transport Network
Bandwidth-intensive computing is attributed to both AI training as well as AI inference, where inference refers to the post-training process in which the model is “ready for the world,” creating an inference-based output from input data using what it learned during the training process. In addition to AI training’s requirements for a large amount of computing power and a large number of high-bandwidth, short connections, there are also foreseen bandwidth requirements beyond the AI data center. To understand how network traffic patterns may evolve beyond the AI data center, let’s review some examples of how the wider transport network was affected by past growth of various applications. Although these applications may not strongly match the effect of AI application traffic, it can provide some insight into the effects that the growth of AI applications may have on optical transport, and thus on the growth of coherent technology.

If we look at search applications, the AI training process is generally analogous to a search engine’s crawling bots combing the internet to gather data to be indexed (AI training being much more computationally intensive). The AI inference process is analogous to the search engine being queried by the end user with results made available for user retrieval with minimal latency. While the required transport bandwidth for search bots and user queries are minimal compared to higher bandwidth applications, the cumulative effect of the search-related traffic is part of the contribution to overall transport traffic, including bandwidth from regional/local caching to minimize latency, as well as usage from subsequent traffic created by acting upon search results.

Understanding how network traffic was affected by the growth of video content delivery is another example that can inform potential AI network transport traffic patterns. A main concern resulting from video content distribution was the burden imposed on the network in delivering the content (especially high-resolution video) to the end-user. To address this concern, content caching, where higher demand content was cached closer to the end-user, was implemented to reduce overall network traffic from the distribution source to the end-user, as well as reduce latency. While it is too early to predict how much network traffic would increase due to expansive queries to and responses from AI inference applications, the challenge is to ensure the latency for this access is minimal. One could see an analogy of content caching to edge computing where the AI inference model is closer to the user with increased transport bandwidth required for these edge computing sites. However, the challenge would be to understand how this would affect the efficiency of the inference function.

Turning to cloud computing for insights on traffic patterns, the rise of (multi-) cloud and computing resulted in intra and inter-datacenter traffic (a.k.a. east-west traffic) increasing as workloads traversed across the datacenter environment. There’s a similar potential rise in this type of traffic with AI as data for training could be dispersed among multiple sites of clusters as well as inference models being distributed to physically diverse sites to reduce latency to end users.

For any of these previous examples, as the demand of these applications increases, the transport bandwidth requirements would also increase from not only the target data (e.g., search results, video), but also from overhead or intra datacenter traffic to support these applications (e.g., content caching, cloud computing, backend overhead). Traffic behavior for aggregating AI training content as well as the distribution of AI inference models and its results may be similar to the traffic patterns of these previous applications, applying pressure to network operators to increase capacity for its data center interconnect, metro, and regional networks. Long haul and subsea networks may also experience a need to expand to meet the demands of AI-related traffic.

Figure 2.  A scenario in which the network fabric physically expands due to facility power constraints, requiring high-capacity optical interconnections.

The Balance of Power and Latency
While the application examples above are related to how the AI application itself may affect bandwidth growth, what is becoming apparent is the power requirements to run AI clusters and data centers are significant. In the past, as the demand for cloud services grew, the need for large-scale data centers to have access to localized inexpensive power sources helped to drive the location selection for large data centers. However, power facility/availability constraints helped drive the adoption of physically distributed architectures, which then relied on high-capacity transport interconnects between data centers to maintain the desired network architecture (Figure 2). We anticipate a similar situation with AI buildouts requiring distributed facilities to address power constraints with potential trade-offs of reduced efficiencies for both AI training and inference. The distributed network would then rely on high-capacity interconnect transport using coherent transmission to extend the AI network fabric. Unlike cloud applications, physical expansion of the network fabric for AI applications has a different set of challenges due to compute and latency requirements for both training and inference.

Figure 3. Extremely low latency is required within the AI cluster to expeditiously process incoming datasets during the training mode. Since datasets are collected before being fed into the training cluster, the process of collecting these datasets may not be as latency sensitive.

As we plan for AI buildouts, one common question is how the physical extension of an AI networking fabric may affect AI functions. While geographic distribution of AI training is not ideal, facility power constraints are certain to lead to a growing adoption of distributed AI training techniques that attempts to mitigate introduced latency effects. As part of the training process, sourcing datasets feeding into the training cluster may not be latency sensitive and would not be as impacted by physical network extension (Figure 3). After training, when the inference model is complete, the goal is to minimize the latency between the user query to the inference model and the transmitted results to the user (Figure 4). The latency is a combination of the complexity of the query as well as the number of “hops” between the inference model and the user. Latency reduction when accessing the inference model, as well as methods to effectively distribute both the training and the inference function beyond a centralized architecture to address single-site power constraints, are ongoing discussions within the industry.

Whether driven by power constraints, dataset sourcing, or inference response efficiency, the sheer growth of AI applications will drive network traffic growth beyond AI cluster sites towards the wider network requiring high-capacity interconnects.

Figure 4.  Minimizing latency for AI inference is a key objective.

Trading off power requirements versus access to inexpensive and abundant power versus latency is familiar territory when it comes to bandwidth intensive applications. The outcome that optimizes these trade-offs is application dependent and can even be deployment-by-deployment dependent. We continue to watch the evolving AI space to see how these network architecture trade-offs will play out, with the impact of how the transport network is designed. High-capacity coherent transport can certainly influence these trade-offs. And as we have already seen, by using coherent high-capacity transport cloud architectures, networks were able to physically expand to alleviate power source constraints by provided fat-pipe links between sites. We anticipate a similar scenario with expanding AI network architectures.

The Ripple Effect
While the near-term focus on high-capacity interconnects for AI applications has been on short reach connections within AI clusters, we are already seeing bandwidth requirements begin to increase, requiring additional coherent connectivity between datacenters supporting AI. And while there is general agreement that the resulting bandwidth demand from AI applications translates to increased traffic across the network, we are at the early stages in understanding how specific segments of the network are affected. Coherent optical interconnects for high-capacity transport beyond the data center already provide performance-optimized transponder solutions at 1.2T per wavelength as well as 400G router-to-router wavelengths moving to 800G using MSA pluggable modules. This technology will continue to play a role in the transport solution supporting AI applications whether the expanding traffic is in the metro portion, data center interconnects, long haul, or beyond.

With data center bandwidth growing rapidly, high-performance pluggable modules have become an important tool for network operators to scale their networks cost-efficiently. Acacia has worked closely with network operators to drive the industry’s first interoperable Probabilistic Constellation Shaped (PCS) interfaces. Acacia’s newest portfolio of silicon-based 800G coherent pluggables has been designed to double the connectivity speed from 400G to 800G to support data center interconnect (DCI) upgrades, taking advantage of next-generation routers with 800G I/O port speeds. When plugged into these routers, this family of 800G pluggables can replace traditional transport equipment across a greater range of infrastructure to meet demand for cloud and AI.

OIF Compliant 800ZR Modules
OIF compliant 400ZR has been a great success for the coherent pluggable industry with multiple suppliers and a tremendous volume of 400ZR QSFP-DD and OSFP modules deployed in metro DCI applications. With the switch and router 800G ports available, 800ZR will further reduce the cost, power, and space per 100G in the same applications. Acacia’s 800ZR pluggables support QSFP-DD and OSFP form factors fully compliant to OIF 800ZR with transmit power variants.

Acacia Delphi DSP-based coherent pluggable modules

800G ZR+ Modules with Interoperable PCS
Acacia’s 800G ZR+ modules are designed to support the recently released OpenROADM specifications that include interoperable PCS transmission capability. The 131Gbaud PCS provides an additional OSNR margin at 800G for longer reach suitable for regional DCI applications, linking multiple fiber spans and in-line amplification between data centers. Acacia 800G ZR+ pluggables support QSFP-DD and OSFP form factors with >1dBm transmit output power.

“The success of ZR+ at 400G was largely driven by its performance and interoperability, which enabled a multi-source environment to emerge,” said Scott Wilkinson, Lead Analyst for Optical Components at Cignal AI. “The interoperability now being proposed with 800G – not only in short distance applications (800ZR), but also in long distance (800G ZR+​) – expands the environment even further. Interoperable PCS will take the market for 800G pluggables beyond simple DCI into regional and even long-haul networks.”

400G QSFP-DD Module for Ultra Long-haul
Expanding Bright 400ZR+ module applications, Acacia has also added a new QSFP-DD for 400G ultra long-haul networks that include 400G QPSK and PCS with various baud rates to fit into different ROADM optical line systems. It is capable of >1dBm transmit power and high transmit OSNR over the entire C-band thanks to the integrated tunable optical filter for amplified spontaneous emission reduction.

Backed by Industry Leading Coherent Technology
Both the 800G pluggable portfolio and 400G ultra long haul pluggable are powered by Delphi, Acacia’s 9^th generation Digital Signal Processor (DSP) ASIC. Acacia boasts the broadest field-proven 400G MSA coherent pluggable portfolio in the industry with more than 250,000 ports shipped based on the Greylock DSP, including more than 10,000 Bright 400ZR+ ports. Acacia’s 800G and 400G pluggable portfolios benefit from Acacia’s 3D Siliconization approach, which applies integration and 3D stacking techniques to enable a single packaged device that includes all the high-speed optoelectronic functions necessary for coherent communications to provide benefits in cost, reliability, power, and size. These devices are manufactured using standard electronics packaging processes and result in improved signal integrity and performance through the reduction of electrical interconnects.

The Delphi DSP-based pluggable modules are planned to be available beginning in Q2 CY2024.

Additional Resources:

Blog: Key Challenges and Requirements for 800G MSA Pluggables

Below is a summary of where you can see Acacia speaking and showcasing its technology at the show.

Acacia Experts Discuss the Latest Trends and Technologies

Sunday, March 24^th

Are Coherent Transceivers About to Experience a Bandwidth Crunch?
Speaker: Long Chen
Time: 1:00 – 3:30 pm
Where: Room 6E

Coherent Optics for Next Generation 100G/200G PON: Single-Carrier or Multi-Carrier?
Speaker: Tom Williams
Time: 400 – 6:30 pm
Where: Room 6E

Monday, March 25^th

Executive Forum at OFC 2024
Status of Photonic-enabled Modules and Interconnects
Speaker: Tom Williams
Time: 10:45 – 12:00 pm
Where: Hilton San Diego Bayfront Hotel

Tuesday, March 26^th

Data Center Summit Panel II: Lowering Power Consumption in Optical Solutions
Organizer: Tom Williams
Time: 2:15 – 3:45 pm
Where: Theater II

Wednesday, March 27^th

CableLabs: Empowering Access Networks with Coherent Optics
Speaker: Tom Williams
Time: 11:30 – 12:30 pm
Where: Theater II

Coherent Optics Unleashed: From 400ZR Success to 800ZR/LR Advancements and 1600ZR Kick-off
Speaker: Tom Williams
Time: 4:00 – 5:00 pm
Where: Theater I

10 Years of Coherent DWDM Pluggables: Past, Present and Future 
Speaker: Christian Rasmussen
Time:  3:00 – 4:00 pm
Where: 3E

Acacia Accepted Papers

M3I. Transmission Optimization
Title: Optical Network Design with High Symbol Rate Flexible Coherent
Transceivers
Acacia Authors: Philippe Jennevé, Valeria Arlunno
Date/Time: Monday, March 25, 2024; 2:30 pm – 3:00 pm
Where: Room 7

W3H. Large Capacity Interconnect
Title: Real-Time 1.2Tb/s Large Capacity DCI Transmission
Acacia Authors: Hongbin Zhang, Shaoliang Zhang, Timo Pfau, Ahmed Awadalla, Mehmet Aydinlik, Jonas Geyer
Date/Time: Wednesday, March 27, 2024; 3:00 pm– 3:15 pm
Where: Room 6F

OIF Interoperability Participation

OIF Interoperability Demo, Booth #1323 – Featuring breakthrough solutions in speed, power and density to meet the growing demands of next-generation data center networking, AI/ML and disaggregation applications. Don’t miss interoperability demonstrations using Acacia’s QSFP-DD 400ZR and Bright 400ZR+ modules (including OpenROADM/ITU-T mode transmission), as well as multi-vendor management demonstrations through Common Management Interface Specification (CMIS).

Meet with Acacia at OFC
If you are attending the show, we welcome the opportunity to meet with you. Click here to request a meeting.  We hope to see you in San Diego!

The longest distance ever reported at single carrier 600G DWDM transmission on an SDM cable
The Amitié submarine cable features Space Division Multiplexing (SDM) technology with 16 fiber pairs, more than traditional subsea cables, with repeater power shared across the fiber pairs to deliver the highest cable capacity. This real-time field trial exceeded any industry trial performance to date with Dense Wavelength Division Multiplexing (DWDM) 800G in a 150GHz channel spacing, equivalent to a spectrum efficiency of 5.33bit/s/Hz and a maximum spectral efficiency of 5.6bit/s/Hz. In addition, 600G was transmitted over 12,469 kilometers for a trans-Atlantic loopback configuration. This is the first time a 140Gbaud single carrier signal was demonstrated live, and is the longest distance ever reported at single carrier 600G DWDM transmission on an SDM cable.

According to Jamie Gaudette, GM of Cloud Network Engineering, Microsoft, “The transmission of 800G over 6,234 kilometers is a milestone that demonstrates SDM cables can deliver increased capacity over traditional subsea cables. This field trial demonstrates what is now a commercial technology for subsea routes, and we can improve the network capacity to help drive digital transformation for people, organizations, and industries around the world.”

“In the era of AI, reliable and fast network connections are more important than ever,” said Bill Gartner, SVP Optical Systems and Optics, Cisco. “Working with Microsoft on the Amitié cable to demonstrate the potential for improved overall network capacity with 800G at these distances is a significant milestone for an SDM cable, and we’re proud to drive the innovations that pave the way for ever increasing network capacity needs.”

Trial Leverages the Latest in Terabit Optics
According to Microsoft and Cisco, this trial was conducted to target improvements in subsea transmission to provide increased performance and capacity. It was performed with the Cisco NCS 1014 platform enabled by Acacia’s CIM 8, which is powered by Acacia’s Jannu digital signal processor and advanced silicon photonics.

CIM 8 features 2^nd Generation 3D Shaping that provides a 20% higher spectral efficiency over the previous generation. CIM 8 also includes advanced non-linear equalization capabilities, an important feature for submarine links. Acacia has been a leader in deployed submarine-capable silicon photonics for almost a decade.

With this recent subsea trial, Microsoft is the latest provider to announce successful transmission with the CIM 8. Previously, China Mobile, NYSERNet, Verizon, and Windstream Wholesale announced their own trials.

Join the Terabit Era
If you’re ready to join the Terabit Era with CIM 8, contact us.

Multiple standardization bodies, including the OIF, Open ROADM, and the IEEE, are working in parallel to standardize 800G optical transmission and 800 Gigabit Ethernet (GbE) protocols, helping to foster economies of scale. In parallel, module vendors are introducing the required technologies to enable low power 120+Gbaud solutions that would fit into small form-factor modules such as QSFP-DD and OSFP.

Higher Baud Rates, Standardization, and Higher Levels of Integration
With the 400G MSA pluggable generation, the industry via OIF converged onto Class 2 ~60Gbaud rate range and 4 bits/symbol 16QAM modulation order to enable 400G transmission within a 75GHz optical spectrum (Figure 1). Open ROADM requirements, targeting service providers, also included the same modulation order and similar baud rates, as well as additional transmission flexibility specifying more modulation modes, such as 2 bits/symbol QPSK to enable longer reaches at 200G.

Figure 1. 2x scaling of baud rates and channel spacing for ~60+Gbaud Class 2 to ~120+Gbaud Class 3 transition.

At 800G, the industry has converged to a 2x scaling of baud rate resulting in Class 3 ~120 Gbaud rates, as shown in Figure 1. Channel spacing requirements double to 150GHz for 800G, providing a straightforward network scaling supporting similar reaches to 400G Class 2 devices. As with 400G, this convergence is expected to drive economies of scale of the technology supporting this baud rate class.

To realize the modulation capability for Class 3 120+Gbaud operation, advancements in both high-speed optical modulation and supporting components as well as high-speed 112G-per-electrical-lane capabilities were needed to enable 800G MSA pluggables in compact form factors.  These optical and electrical high-speed capabilities have already been proven with the introduction of Acacia’s performance-optimized Coherent Interconnect Module (CIM) 8 module which utilizes silicon photonics, high speed ADC/DACs, RF components, and Acacia’s 3D Siliconization for Class 3 120+Gbaud transmission. The high-level of integration from 3D Siliconization allows this high baud rate technology to fit into QSFP-DD and OSFP pluggable form-factors, all while maintaining high signal integrity and low power consumption.

Figure 2.  3D Siliconization used in (left to right) Class 2 MSA Pluggables and Class 3 performance-optimized CIM 8. Highly integrated co-packaging is going to be important for Class 3 800G MSA pluggable modules.

Key Features Needed for 800G MSA Pluggable Modules
To meet customer needs and drive future adoption, 800G coherent MSA pluggables should have a number of key features and capabilities related to optical transmission, client traffic, low power consumption, and interoperable module management.

Figure 3. Illustrating the key features needed for 800G MSA Pluggable modules.

Optical Transmission Features

OIF 800ZR and high-performance interoperable PCS modes. OIF is defining an interoperable standard performance 800ZR variant addressing coherent line interfaces for amplified, single span, DWDM links over 80km using Class 3 optics operating at ~4 bits/symbol (equivalent to 16QAM) modulation. For a higher performance 800G solution, Open ROADM is defining enhanced performance modes that include an interoperable probability constellation shaping (PCS) implementation utilizing both Ethernet and OTN framing.

Multi-haul capable. In current Class 2 ~60Gbaud MSA pluggable solution designs capable of adjusting the modulation mode, a long reach 200G capability is available by setting the modulation order to QPSK (2 bits/symbol) rather than 16QAM (4 bits/symbol) used for 400G transmission. This capability was standardized in Open ROADM and adopted by OpenZR+. Class 3 ~120Gbaud solutions can be used for 800G metro/regional reaches, and for multiple different standard and proprietary modes at 400G and 600G to address a wide range of network requirements.

High transmit optical power capability. Like high-Tx (>0dBm) optical power capabilities introduced in Acacia’s Bright 400ZR+ QSFP-DD modules, 800G coherent MSA modules will require optical amplification to operate over traditional brownfield networks with ROADM network elements. Internal optical amplification is a key feature variant for this generation to support these types of networks.

Client Traffic Features

800GbE client traffic support. A key client traffic protocol to be supported in 800G generation coherent MSA pluggables is 800GbE. IEEE P802.3df^TM aims to define the requirements for native Ethernet traffic at 800G data rates. To support native 800G Ethernet traffic from switch/router I/O ports, 800G generation coherent MSA pluggables are required to support this protocol.

Multiplexing lower speed 100/200/400GbE electrical client traffic. It is expected that when 800G coherent MSA pluggables are introduced, 100GbE, 200GbE, and 400GbE will continue to be widely deployed client traffic speeds. Therefore, 800G pluggables need to support the ability to multiplex these lower speed protocols into 800G transmission, with requirements being established by the standardization groups. For networks utilizing OTN, support for FlexO at 800G could be possible.

Power Consumption and Management

Low power consumption. As with other MSA pluggable solutions, optimizing for low-power operation is a priority. The leveraging of Moore’s law with decreasing CMOS node sizes along with increased ASIC functionality has been a reason for the success of coherent pluggables—providing high-capacity links in a small form-factor. Power-optimized designs continue to be a priority for the new generation of Class 3 baud rate coherent MSA pluggables, not only for compliance in 800G slots, but also for backwards compatibility into lower-rate 400G legacy ports which have more restrictive power consumption requirements.

Content Management Interoperability Services (CMIS) compliance. In addition to industry standardization efforts at the optical transmission and client traffic levels, there has been a concerted effort to ensure multi-vendor interoperability of the module management interface through CMIS, defined in OIF. This ensures a common and predictable management signaling interface between the module and the host switch/router from one module vendor to another. CMIS compliance, a key requirement for 400G MSA modules, is going to extend to 800G as well.

Interoperable PCS Modes

Taking a page from the performance-optimized coherent playbook, 800G MSA pluggable solutions are expected to introduce interoperable PCS optical transmission. PCS shapes the optical transmission using an algorithm that weights the constellation to utilize the inner points more than the outer points, resulting in improved OSNR performance with a minimal increase in overhead. While previous implementations of PCS have always been proprietary, several key DSP vendors have collaborated over the last 12 months to enable the industry’s first introduction of interoperable PCS for 800G MSA pluggables.

Figure 4. High-level block diagram comparing 800G MSA pluggable solutions utilizing 800ZR standard transmission and 800ZR+ interoperable PCS mode for higher OSNR performance.

Driven by Open ROADM, the 800G interoperable PCS implementation provides a power-optimized method to boost the performance beyond 800ZR, similar to how oFEC boosted the performance beyond 400ZR in OpenZR+ modules. This additional performance allows 800G implementations to achieve similar reaches as 400G implementations based on 16QAM transmission. This Open ROADM interoperable PCS mode operates in the 130+Gbaud range, which is slightly higher than the 800ZR mode, but can still enable transmission in 150GHz channels. With interoperable PCS, network operators can benefit from a greater range of network implementations from the initial 800G MSA pluggable offerings compared to the initial 400G point-to-point offerings of the previous generation.

Following the Right Path to 800G Pluggables

In summary, operators are looking for the following key functional requirements to transition to 800G coherent MSA pluggables.

• Support for OIF 800ZR and high-performance interoperable PCS modes
• Multi-haul capable
• High Tx optical power option
• 800GbE client traffic support
• Multiplexing lower speed 100/200/400GbE electrical client traffic
• Low power consumption
• CMIS compliance

This solution can plug directly into switch/router ports to further drive adoption of IP-over-DWDM router-based optical network architectures. The first 800G pluggable deployments are expected in 2024.

To date, multiple system vendors have converged around Class 3-based solutions (Figure 1), recently announcing their next generation offerings. This industry convergence creates the benefit of economies of scale and broad industry investments into the technology used in this baud rate class, the same class being used for 800G MSA pluggable solutions.

Figure 1.  Acacia and other coherent vendors have announced Class 3 Terabit Era solutions.

Advancements Resulting in 65% Power-per-Bit Savings Over Current Competing Solutions
Doubling the baud rate from Class 2 to Class 3 in silicon was a significant engineering achievement, combining design advancements in high-speed Radio Frequency (RF) and Analog to Digital Converter (ADC) and Digital to Analog Converter (DAC) components plus well-designed co-packaging integration of silicon and silicon photonic (SiPh) components. These achievements led to Acacia’s successful 140Gbaud in-house capability that is being leveraged in the commercially available CIM 8 solution.

With high-volume shipments of multiple coherent Class 2 module products utilizing Acacia’s 3D Siliconization, this proven co-packaging integration solution provided the foundation for extending this capability to Class 3 140Gbaud implementation utilized in the CIM 8 (Figure 2). 3D Siliconization maximizes signal integrity by co-packaging all high-speed components including the coherent Digital Signal Processor (DSP) application-specific integrated circuit (ASIC), transmitter and receiver silicon photonics, and 3D stacked RF components into a single device that is manufactured in a standard electronics packaging house. Silicon technology has demonstrated cost and power advantages over alternative technologies, making it the material system of choice for these higher baud rates. These advancements enabling a doubling of the baud rate have led to a 65% power-per-bit savings of CIM 8 over current competing solutions that utilize alternative optical material systems. In addition, the size and power savings of this latest generation enabled the ability to house this 1.2T 140Gbaud solution in a pluggable form-factor.

Figure 2.  An example of 3D Siliconization used in the CIM 8 module, resulting in a volume electronics manufacturable high-speed single device larger than a quarter.

2^nd Generation 3D Shaping Advances Coherent Performance
The CIM 8 is powered by Jannu, Acacia’s 8^th generation coherent DSP ASIC. The design greatly expands on the success of the Pico DSP ASIC predecessor used in the widely deployed performance-optimized Class 2 AC1200 module (Figure 1). The AC1200 was the first module to introduce 3D Shaping, which provided finely tunable Adaptive Baud Rate up to 70Gbaud as well as finely tunable modulation up to 6 bits/symbol. The AC1200 had achieved record breaking spectral efficiency at the time of its introduction, as evidenced by a subsea trial over the MAREA submarine cable connecting Virginia Beach, Virginia to the city of Bilbao in Spain. Finely tunable baud rate helps maximize spectral efficiency in any given passband channel, converting excess margin into additional capacity/reach, and avoids wasted bandwidth due to network fragmentation.

Figure 3.  A popular feature is the fine-tunability of baud rate introduced by Acacia with the Class 2 AC1200; CIM 8 incorporates the same Adaptive Baud feature (as part of 2^nd Generation 3D Shaping) for Class 3 baud rate tunability.

The 5nm Jannu DSP ASIC in CIM 8 intelligently optimizes optical transmission using 2^nd Generation 3D Shaping with an increased Adaptive Baud Rate tunable range up to 140Gbaud, as well as finely tunable modulation up to 6 bits/symbol using enhanced Probabilistic Constellation Shaping (PCS). With 2^nd Generation 3D Shaping, the CIM 8 module can achieve a 20% improvement in spectral efficiency.

Terabit Era Solutions Provide Full Network Coverage
Class 3 technology not only ushers in the terabit era, but also enables full multi-haul network coverage as the high baud rate capabilities transport nx400GbE client traffic across a service provider’s entire network. Full network coverage is not only enabled by adjustment of the modulation, but also implies the capability to optimize for various network conditions which include overcoming transmission impairments.

Figure 4. CIM 8 1.2T, 1T, 800G, and 400G transmission constellations operating at Class 3 baud rates providing wide network coverage addressing multiple applications.

CIM 8 offers significant power-per-bit reductions as well as cost efficiencies for various optical network transport applications.

DCI/Metro Reaches
For transporting 3x400GbE or 12x100GbE client traffic with metro reaches in a single carrier, the CIM 8 is tuned to ~6 bits/symbol (equivalent to 64QAM, example constellation on left). Data center interconnect (DCI) applications would take advantage of this high-capacity 1.2T transport capability to tie data center locations together. This amounts to 38.4T per C-band fiber capacity.

Long-Haul Reaches

For transporting 2x400GbE with long-haul reaches, the CIM 8 is tuned to ~4 bits/symbol (equivalent to 16QAM, example constellation on the right). Wide 800G network coverage is achieved with the Class 3 140Gbaud capabilities enabling service providers to provide end-to-end 2x400GbE, 8x100GbE, or native 800GbE transport across their networks, covering essentially all terrestrial applications.

Ultra-Long-Haul/Subsea Reaches

And for ultra-long-haul/subsea reaches, the CIM 8 is tuned to ~2 bits/symbol (equivalent to QPSK, example constellation on the left). As with the previous scenarios, spectral efficiency with a wavelength channel is optimized by fine-tuning of the baud rate. These high spectrally efficient modes can carry mixed 100GbE and 400GbE traffic over the longest subsea routes in the world with lowest cost per bit. It’s worth noting that almost a decade ago, Acacia demonstrated SiPh capabilities for subsea coherent deployments. CIM 8 incorporates second generation non-linear equalization (NLEQ) capabilities to mitigate the non-linear effects of optical transmission especially for these ultra-long-haul/subsea links providing additional OSNR.

In all the above scenarios, the CIM 8 utilizes advanced power-efficient algorithms to compensate for chromatic and polarization dependent dispersion. In addition, the module accounts for coverage of aerial fiber network segments that require fast state-of-polarization (SOP) tracking and recovery due to lightning strikes. The SOP tracking speed of CIM 8 is double the speed of its predecessor. This fast SOP tracking feature can also be utilized for sensing applications.

Network Operators Achieve Record Breaking Field Trials with CIM 8
CIM 8 capabilities have already been put to the test as illustrated by multiple record breaking field trials across a wide range of applications. These include >5600km 400G transmission over a mobile carrier’s backbone network, 2200km 800G transmission over a research and education network, and >540km 1T transmission over a wholesale carrier’s network.

Acacia continues to demonstrate its technology leadership by leveraging mature knowledge in proven silicon-based coherent technology, producing the first shipping coherent solution to lead the industry into the Terabit Era with the 1.2T pluggable CIM 8 module. With the breakthrough capability of 140Gbaud transmission along with the advanced Jannu DSP ASIC using 2^nd Gen 3D Shaping and leveraging 3D Siliconization, network operators can support full network coverage for multi-haul applications, especially to support growing demands for nx400GbE and upcoming 800GbE traffic.

References:
Blog: Terabit Today: Maximize Network Coverage
Blog: How Industry Trends are Driving Coherent Technology Classifications
Blog Series: The Road Ahead for Next-Generation Multi-Haul Designs Part 1, Part 2, Part 3

Arelion Achieves 64% CAPEX and 76% OPEX Savings Enabled by Bright 400ZR+ Deployment

In August 2023, Arelion announced that it has taken another landmark step in converging its IP and optical layers as the first global network to deploy 400G QSFP-DD ZR+ Bright coherent optical modules in its production #1 ranked IP backbone. This first regional reach deployment spans 675 kilometers between Stockholm and Copenhagen over third-party Optical Open Line System (O-OLS). According to Arelion, the streamlined architecture eliminates the need for excessive hardware, thereby reducing potential points of failure. As a result, it achieves 64% CAPEX and 76% OPEX savings. This contributes to a significantly more cost-efficient network with fewer interfaces to control and maintain.

Highlighting the benefits of these modules, Arelion’s Mattias Fridström shares his insights in this video from testing the technology to how they can potentially transform network infrastructures.

Mattias Fridström, Vice President & Chief Evangelist at Arelion shares the benefits of deploying Acacia’s 400G QSFP-DD Bright Optical Modules in Arelion’s production IP backbone

Dariusz Solowiej, VP Network Technology & Customer Operations at Arelion added, “With constantly rising demand for our IP services and increasing traffic across the Internet, Arelion is constantly looking to deploy the latest technology. The deployment of 400G QSFP-DD Bright Optical Modules will ensure cost-effective, high-performance connectivity for our customers and help us grow our network in scale as we continue to connect the world. In addition, the coherent pluggable modules also help us achieve our sustainability goals through improved energy efficiency and redeploying redundant hardware assets.”

CENIC Validates Coherent Pluggable Optics for Big Data Applications
Using Bright QSFP-DD coherent optics, the Corporation for Education Network Initiatives in California (CENIC) turned up a 300 Gbps optical service over CENIC’s production line system between Los Angeles and Sunnyvale and confirmed the error-free performance of the service with a comfortable operating margin.

According to CENIC, the new-generation coherent pluggables integrate an amplifier, making it possible to transmit from the optic at power levels that match those of typical transponder line cards. As a result, external amplification is no longer needed to boost the power level transmitted from the optic before it reaches the optical line system.  As explained by Sana Bellamine, CENIC’s Director of Regional and International Infrastructure, “The elimination of the external amplification requirement is an important step toward simplifying the provisioning of optical services and facilitates the adoption of coherent pluggables over our production line system.”

CENIC Validation Setup Diagram with Bright ZR+ Coherent Pluggables with Integrated Amplifiers

Announced earlier this year, Vodafone Turkey and Sipartech trials are summarized in this article.

Bright 400ZR+ QSFP-DD Modules Expands Applications by Enabling Longer Reach Applications
With an optical transmit power at least 10X greater than 400ZR, Bright QSFP-DD modules enable network operators to expand applications that can be addressed by 400G coherent pluggables in router-based optical deployments to include brownfield and greenfield metro/regional networks with reconfigurable optical add-drop multiplexer (ROADM) nodes.

Bright 400ZR+ QSFP-DD modules expand applications of 400G coherent pluggable to brownfield and greenfield metro/regional networks with ROADM nodes.

Visit Us at ECOC OIF 400ZR+ Interop Demonstration
If you are attending ECOC and want to see the Acacia Bright ZR+ coherent module in action, check out the 400ZR+ optics interoperability demonstration at the OIF Booth #304.  We hope you see you there!

Additional Resources

• Blog: Brightening ROADM Networks
• Product Page: Bright 400ZR+ coherent pluggable QSFP-DD module

400G Pluggables and Terabit Era Optics
The 400G coherent pluggable market has been the fastest growing coherent technology to date and, according to CignalAI, as of 2022, Acacia’s comprehensive 400G ZR/ZR+ portfolio is leading the market with 60% market share.

Acacia’s  Bright 400ZR+ QSFP-DD pluggable coherent optical module with high-transmit power is in high demand with a steady stream of trials and deployments. Leading up to ECOC, we saw Bright deployments announced from Arelion and the Corporation for Education Network Initiatives in California (CENIC) and earlier this year, Vodafone Turkey and Sipartech announced their own Bright field trials.

While pluggables or router-based DCOs (Digital Coherent Optics) are becoming popular for requirements in DCI, metro and some long-haul applications, transponder-based coherent solutions are still being used for long-haul, ultra-long haul and subsea. Acacia’s performance optimized multi-haul coherent solutions have proven to be extremely effective for these applications. Our single carrier pluggable 1.2T Coherent Interconnect Module 8 (CIM 8), shipping since late 2022, is leading the industry into the Terabit Era. To date, we have seen record-breaking CIM 8 field trial announcements from Nysernet, China Mobile and Windstream Wholesale.  The CIM 8 enables these network operators to achieve the highest capacity and reach today while maximizing transmission data rate across a wide range of multi-haul network applications.

Defining the Path to 800G Pluggables
Following the explosive growth of 400G pluggables, next-generation switch/router ASICs are being introduced with 800G I/O port speeds, creating the need for 800G optical interfaces for DCI. Like the 400G MSA pluggable cycle, multiple standardization bodies such as OIF, Open ROADM and the IEEE are working in parallel to provide industry standards for 800G optical transmission and 800 Gigabit Ethernet (GbE), helping to foster economies of scale. While module vendors are introducing the required technologies to enable low power 120+Gbaud solutions that would fit into small form-factor modules such as QSFP-DD and OSFP.

To meet customer needs and drive future adoption, it’s important for 800G coherent MSA pluggables to have several key features and capabilities including optical transmission, client traffic, low power consumption, and interoperable module management.  We believe the key functional requirements that operators are looking for to make this transition include:

• Support for OIF 800ZR and high-performance interoperable Probabilistic Constellation Shaping (PCS) modes
• Multi-haul capable
• High transmit (Tx) optical power option
• 800GbE client traffic support
• Multiplexing lower speed 100/200/400GbE electrical client traffic
• Low power consumption
• Coherent Common Management Interface Specification (C-CMIS) compliance

With the first 800G pluggable deployments expected in 2024, these future solutions can plug directly into switch/router ports to further drive adoption of IP-over-DWDM router-based optical network architectures.

Coherent Interoperability Participation:  OIF and OpenZR+ MSA
Continuing its commitment to building an industry-wide ecosystem, Acacia is excited to be participating in the OIF’s largest-ever multi-vendor interoperability event in booth #304 at ECOC. Come see our participation in the 400ZR+ optics and Common Management Interface Specification (CMIS) implementations interoperability demonstrations.

In addition, Acacia has continued to play a key role as a member of the OpenZR+ Multi-Source Agreement (MSA) Group. Leading up to ECOC, the group announced that it had published the OpenZR+ Rev 3.0 specification, which defines a higher performing 400G 8QAM mode as well as a higher transmit power mode. This new specification is designed to further expand the application space for OpenZR+ with new modes that can address longer reaches and a wider range of network architectures.

Come See Us!
If you are attending the show and want to connect, we’d welcome the opportunity to meet with you. Click here to set up a meeting. We hope to see you in Scotland.

Class 3 Baud Rate Solutions Provide Wide Network Coverage to Support nx400GbE
As widely known in the industry, the two primary “knobs” for optimizing coherent transmission capacity and reach are the baud rate and the bits/symbol modulation order. While rapid advances to increase capacity have pushed the upper modulation order to the current 6 bits/symbol (equivalent to 64QAM), further increases in modulation order provide incremental improvements in spectral efficiency with significant reductions in network coverage. Because of this, the industry focus to reduce cost and power consumption per bit has shifted toward achieving higher baud rate modulation per wavelength. Technology advancements that resulted in achieving 120+Gbaud coherent modulation speeds, as Figure 1 illustrates, have enabled a new generation of Class 3 capabilities which have propelled the industry from gigabit to terabit transmission capacity.

Figure 1. Achieving Class 3 baud rates enabled coherent transport solutions to break through the terabit threshold, ushered in by Acacia’s CIM 8 solution.

Terabit era performance-optimized solutions such as Acacia’s shipping Coherent Interconnect Module 8 (CIM 8), powered by the Jannu DSP, as well as announced solutions from several other optical transport vendors are now leveraging this Class 3 baud rate standardization. While this operating baud rate class enables a capacity of 1.2T for metro/DCI reaches, a key benefit is the ability to provide full network coverage at 800G to support transport of 2x400GbE clients, as shown in Figure 2. In addition, subsea applications can also be supported with greater flexibility to achieve optimal spectral efficiency. The flexibility, full coverage, and availability of these terabit era solutions make them attractive for supporting evolving transport needs as native 400GbE traffic requirements are becoming more commonplace.

Figure 2. Class 3 terabit era CIM 8 from Acacia provides 800G everywhere to transport 2x400GbE client traffic. By adjusting the transmission bits/symbol, a higher or lower number of 400GbE links can be achieved with corresponding reaches.

The CIM 8 achieves Class 3 140Gbaud rate capability using proven silicon technology to successfully break through the terabit-per-wavelength threshold. Silicon technology has demonstrated cost and power advantages over alternative technologies, making it the material system of choice for these higher baud rates. This module enables a coherent transmission solution capable of providing full network coverage to support nx400GbE traffic.

Terabit Era Solutions Support 400GbE Today, Ready for 800GbE in the Future
Supporting 400GbE client traffic over a network operator’s transport infrastructure is expected to be the dominant trend for many years to come. Terabit era solutions are ideal for these providers because they can implement a straightforward 2x scaling of channel spacing to evolve from Class 2 to Class 3 technology, as illustrated in Figure 1.

With full network coverage at 800G using ~4 bits/symbol transmission, the CIM 8 module can not only support today’s 2x400GbE client traffic, but it is also ready to enable 800GbE interconnections when that end-user demand materializes in the future.

With More than 65% Power-per-bit Savings, Why Delay on Achieving Power Reduction Goals?
CIM 8 takes advantage of Acacia’s most advanced silicon photonics technology that enables 140Gbaud capabilities resulting in doubling the capacity of each wavelength without doubling the component count, size, and power of the coherent device. In addition, advancements such as Acacia’s 3D Siliconization, which leverages highly integrated opto-electronic packaging, as well as the adoption of power-efficient signal processing algorithms, all contribute to a 65% power-per-bit savings of CIM 8 over current competing solutions being deployed.

With the industry striving to reduce overall power consumption, adoption of available solutions such as the Acacia CIM 8 can help towards achieving these goals sooner. Delaying the deployment of power saving technology on a network-wide scale can result in continued carbon emissions at current levels, delaying the achievement of power consumption reduction goals.

By incorporating coherent technology innovations to achieve low power Class 3 140Gbaud transmission while leveraging volume processes, CIM 8 is a result of the investments Acacia has made over generations of silicon-based products, providing a significant advantage for providers looking to drive long-term power-per-bit reductions without sacrificing performance and reach.

Maximizing Coverage for the Long-Term with Terabit Era Solutions
Network operators have multiple options to consider when migrating their infrastructures to support the growth of nx400GbE client traffic and preparing for 800GbE. While router-based optics solutions are gaining momentum, those wanting to maintain a transport optical layer are looking towards terabit era performance-optimized coherent solutions such as Acacia’s CIM 8 to support this growth. The CIM 8 module is shipping today and not only provides flexibility in supporting nx400GbE client traffic with wide network coverage, but also follows the direction of industry baud rate standards that allow for scalable network/channel-spacings as well as the utilization of mature silicon technology. This enables service providers to future proof their networks for traffic demands, while optimizing their return on investment and minimizing risk.